Heat sealing apparatus

ABSTRACT

Apparatus for heat sealing sheets of thermoplastic material is constructed with a Nichrome strip constituting the heated die element. The die strip is mounted to the movable press element, with one end fixedly secured thereto, and the other end of the strip being free to move longitudinally as the strip temperature increases. The motion of the strip is transmitted through a motion multiplying linkage to operate a movable contact out of engagement with a stationary contact when the strip has reached a predetermined temperature, which will occur after sufficient heat for sealing has been applied and prior to the application of excessive heat. The movable contact is automatically latched in the open position to maintain the flow of heating power to the strip interrupted at the end of the sealing operation. The latch releases the movable contact when the cooled strip is moved out of sealing position so that when the strip is next moved to sealing position the movable contact automatically engages the stationary contact to complete the heating circuit for the strip.

United States Patent Farkas [151 3,655,487 [451 Apr. 11, 1972 [541 HEATSEALING APPARATUS [72] Inventor: Robert D. Farkas, 5601 First Ave.,

Brooklyn, N.Y. 11215 [22] Filed: Mar. 9, 1970 [2l] Appl, No.: 17,373

[56] References Cited UNITED STATES PATENTS 2,961,031 11/1960 Fener..156/380 3,234,072 2/1966 Dreeben 156/583 X 3,262,833 7/1966 Zelnick..156/583 Primary Examiner-Samuel Feinberg Assistant Examiner-J. J.Devitt Attorney-Ostrolenk, Faber, Gerb & Soffen [57] ABSTRACT Apparatusfor heat sealing sheets of thermoplastic material is constructed with aNichrome strip constituting the heated die element. The die strip ismounted to the movable press element, with one end fixedly securedthereto, and the other end of the strip being free to movelongitudinallyas the strip temperature increases. The motion of thestrip is transmitted through a motion multiplying linkage to operate amovable contact out of engagement with a stationary contact when thestrip has reached a predetermined temperature, which will occur aftersufficient heat for sealing has been applied and prior to theapplication of excessive heat. The movable contact is automaticallylatched in the open position to maintain the flow of heating power tothe strip interrupted at the end of Athe sealing operation. The latchreleases the movable contact when the cooled strip is moved out ofsealing position so that when the strip is next moved to sealingposition the movable contact automatically engages the stationarycontact to complete the heating circuit for the strip.

ll Claims, 4 Drawing Figures HEAT SEALING APPARATUS This inventionrelates to heat-sealing apparatus in general and more particularlyrelates to impulse type heat sealing apparatus of particularly simpleconstruction and operation.

Heretofore, apparatus for heat sealing thermoplastic material has notbeen practical as a toy or household item. That is, apparatus utilizinghigh frequency current for heat sealing is relatively expensive even forlight duty apparatus. Impulse sealing apparatus, though considerablyless expensive than high frequency apparatus, has proven to have manydrawbacks in the case of a stripped-down machine operated byinexperienced personnel. ln particular, the quality of the heat seal isa function of temperature, pressure, and length of time during which thetemperature and pressure are applied. In fact, it has been foundnecessary to automatically control the cut off of heating power toprevent imperfect sealing due to excessive heat.

ln order to accomplish this is an inexpensive manner, the instantinvention utilizes a strip of resistance heater material as the heateddie. With the strip in sealing position one end thereof is rigidly xedin position, while the other end is free to move longitudinally as thestrip expands upon heating thereof. This expanding motion-is transmittedthrough a motion multiplying linkage to automatically'open the heatercircuit for the die when the heated die reaches a predeterminedtemperature. The contact is latched open and is not permitted to recloseuntil the die is first lifted from the work and then brought down intosealing position.

Heating power is automatically applied to the die when the latter isbrought into sealing position. Operation of the switch or contact meansthrough the expansion of the die element automatically interruptsheating power after a sufficient amount, but not an excessive amount, ofheat is applied to the plastic material for sealing thereof. A lampconnected in parallel with the die indicates when heating power is beingapplied to the die. The operator is instructed to maintain the die insealing position for a short period of time after heating power isdiscontinued. During this period the die cools and the molten plasticmaterial at the seal line solidies to provide the seal.

The sealing die strip is extremely thin so that relatively low power isrequired for heating, and the die reaches sealing temperature in arelatively short time and cools rapidly.

Accordingly, a primary object of the instant invention is to providenovel inexpensive heat sealing apparatus.

Another object is to provide heat sealing apparatus of the impulse typehaving novel means for automatically controlling the application anddiscontinuance of heating power through the sealing die.

A further object is to provide impulse heat sealing apparatus in whichthe sealing die consists of a strip of resistance heater material, oneend of which if fixed and the other end of which is free to movelongitudinally as the strip is heated, so as to automatically open aswitch to interrupt heating power to the strip, by utilizing a linkageproviding mechanical amplification.

These objects as well as other objects of this invention will becomereadily apparent after reading the following description of theaccompanying drawings in which:

FIG. 1 is a perspective of heat sealing apparatus constructed inaccordance with the teachings of the instant invention with the elementsthereof in the open or work loading and unloading position.

FIG. 2 is an enlarged cross section taken through line 2-2 of FIG. llooking in the direction of arrows 2-2 with the elements in the closedor sealing position.

FIG. 3 is an enlarged perspective of the motion multiplying linkage inthe apparatus of FIG. l.

FIG. 4 is a fragmentary plan view showing the relation between theresistance heater die strip and the cooperating anvil when the apparatusis in sealing position.

Heat sealing apparatus includes relatively stationary support or base 1lhaving L-shaped brackets l2 secured thereto and extending along the rearedge thereof. Hinge means 13 extending along the upper edge of bracket12 pivotally mounts movable support 14 to base ll. A plurality of leafspring l5 secured to the inner surface on the vertical leg of bracketl2, bias movable support 14 to the'open position relative to base 14(FIG. 1). In this open position of apparatus l0, die 20 is relativelydistant from anvil 16 so as to permit insertion and removal of workconsisting, typically, of two sheets 2l, 22 of thermoplastic material(FIG. 2) that are to be bonded together by one or more heat seals.

Movable support 14 is pivotable counterclockwise with respect to FIG. labout hinge 15 toward base l1 to the sealing position shown in FIG. 2wherein the Teflon impregnated glass cloth lower surface covering 23 ofdie strip 20 engages upper work sheet 22 and forces lower work sheet 21into firm engagement with upper edge 17 of anvil 16. A pair of stops 18,19, secured to base 11 and extending upward therefrom, limit movement ofsupport 14 toward base 11 so that the force exerted by anvil 16 and die20 on the work material 2l, 22 will not cause excessive compression atthe heat seal area where bonding takes place.

Anvil 16 is operatively positioned on upper surface 11b of base 11 bydownward indexing formation 16a that is received by cooperating indexingformation 11a in base l1. Legs l6b, along the sides of anvil 16 near thebottom thereof, rest against upper surface 1lb to stabilize anvil I6when downward force is applied thereto.

Also mounted on the upper surface 1lb of base 1 1 is insulating block 26having stationary contact 27 mounted on the forward surface thereof.Contact 27 is part of switch means 30 that also includes movable contact28 formed by the bent lower end of flexible rod-like switch actuator arm3l having pivot pin 32 secured thereto at a point intermediate the endsthereof and extending transverse thereto. Pivot pin 32 extends into aclearance aperture in the downwardly extending leg of bracket 33 securedto the inner surface of movable support 14. A pair of spring retainers34, received by spaced annular recesses (not shown) in pin 32, arepositioned on opposite sides of the downwardly extending leg of bracket33 to retain pin 32 mounted to bracket 33 and freely rotatable withrespect thereto.

Upper end 35 of arm 31 extends through clearance aperture 36 at the rearend of bar 40 which rests against the upper surface of spring retainer99 mounted on arm 31. Contact spring 41, secured to the upper surface ofbar 40, engages the upper end 35 of arm 3l to maintain electricalcontact between bar 40 and arm 3l. As will hereinafter be seen, thelocation of pin 32 closer to bar 40 than to contact 27 provides motionmultiplication of the movement for bar 40.

The forward end of bar 40 is pivotally secured by rivet 91 to free end20a ofthe elongated resistance heater strip (typically Nichrome)comprising die 20. The other end 20b of die 20 is fixedly secured toinsulating block 46 mounted to the inner surface of movable support 14.Pin 47 extends through the most forward aperture in the set of threeclearance apertures 14a in movable support 14 and through the mostforward aperture in the set of three clearance apertures 40a in bar 40,and cooperates with spring retainer 48 to pivotally mount bar 40 formovement parallel to the inner surface of movable support 14 in positionadjacent to such inner surface. Head 47a of pin 47 is disposed within arecess in the upper surface of movable support 14.

With the elements of heat sealing apparatus l0 in the position of FIG.-l, movable support 14 is raised and switch 30 is open in that movablecontact 28 is separated from stationary contact 27. After the workconsisting of thermoplastic sheets 2l, 22 is placed on the upper edge 17of anvil 16, support 14 is pivoted counterclockwise against the forcesof opening spring 15 until the inner surface of support 14 engages theupper surfaces of stops 18, 19. During this downward movement contact 28initially engages the cam formed upper surface 26a of insulator 26 whichdeflects arm 31 so that the lower end thereof, hence contact 28, movesforward past the upper edge of stationary contact 27 to the solid lineposition of FIG. 3 wherein switch v30 is closed. This completes acircuit extending from insulation covered conductor 5l, through switch30, arm 31, spring contact 41, bar 40, die and insulation coveredconductor 52. With switch closed, conductors 51, 52 connect theelongated strip resistance element constituting die 20 to the secondaryof transformer 55 to supply electrical energy which generates heat indie 20.

As die 20 heats up, thermal expansion thereof` is, for the most part,directed longitudinally. Since end 20b is in fixed position, end 20amoves to the right (direction of arrow A in FIGS. 1, 3 and 4) and actsthrough motion multiplying linkage 30, 40 to separate the contacts ofswitch 30. That is, as die end 20a moves in the direction of arrow A bar40 is pivoted in a counterclockwise direction looking down at the top ofpin 47. This moves upper end 35 of arm 31 to the left with respect toFIG. l causing contact 28 to wipe across the forward surface ofstationary contact 27. When contact 28 reaches the near edge of contact27 as viewed in FIG. 3, the self biasing of contact arm 31 forcescontact 28 to the rear of contact 27 (phantom position of FIG. 3). Asdie 20 cools with die 20 in sealing position insulator 26 acts as alatch to block return movement of stationary contact 28 despite theforce of contraction and the force exerted by tension spring 52connected between arm 40 and support member 14.

By the time contact 28 separates from contact 27 in this manner, thetemperature of die 20 has reached a sufficiently high level to cause alocalized area of work sheets 21, 22 to become plastic and to fusetogether provided sufficient heat is maintained for a sufficient periodof time. The opening of switch means 30, hence deenergization of die 20,is indicated by the extinction of pilot light 49 mounted on the uppersurface of support 14 and connected in electrical parallel with die 20Sealing time may be adjusted by changing the location of the pivot forbar 40. More particularly, the three-hole group of openings 40a is inalignment with the three-Hole group 14b in support 14. With pin 47 inthe position closest to the end of bar 40 closest to die 20, motion ofdie end 20a is subjected to the greatest motion multiplication in theoutput at the other end of bar 40 where it connects to switch arm 31.Similarly with pin 47 in the hole 40a most distant from die end 20a,heating time is increased to the maximum in that multiplication ofmovement for die end 20a is the least of the three positions for pin 47.

Typically upper edge 17 of anvil 16 is one half inch long by onesixteenth inch wide, die 20 is one quarter inch wide by 3 inches long by0.001 inch thick, and Teflon cover 23 is 0.005 inch thick. Energizingdie 20 to draw 6 amps from a 3% volt source, the application of heatingpower for l second is sufficient to heat seal two 0.010 inch thicklayers of polyvinyl chloride.

It is noted that while anvil 16 is shown as providing a rectangular sealcorresponding to edge 17, other anvil shapes, such as stars, diamonds,etc. may be used to provide seals in these shapes for decoratingpurposes. Changing an anvil is simply a matter of lifting its indexingextension from indexing recess 1 la in base ll and inserting theindexing extension of another anvil into recess l la.

It is noted that switch 30 may be replaced by a commercially availablepush button operated switch biased to open position with the self biasof arm 31 being sufficient to overcome the switch biasing forces andmaintain the switch when arm 3l is engaged with the free end of the pushbutton. The lower end of arm 31 will slide across such free end, butwill automatically drop off when a good heat seal is made and be latchedagainst the side of the push button as the latter moves forward to opencircuit position. Such commercially available switch may be connected tointerrupt the transformer primary in which event die 20 will bepermanently connected to the secondary.

While die 20 and other current carrying elements have been illustratedas being mounted to movable support 14, it should be apparent to thoseskilled in the art that many, if not all, of the current carryingelements may be mounted to bed ll and anvil 16 may be secured to movablesupport 14.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now be apparent tothose skilled in the art. Therefore, this invention is to be limited,not by the specific disclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. Heat sealing apparatus including first and second support sections;means mounting said sections for relative movement between a closed, orsealing, position and an open, or work loading and unloading, position;heat sealing means including a die mounted to said first section andelectrically energized first means for heating said die; switch meansconnected in circuit with said first means for controlling energizationthereof; said switch means being operated automatically to closedcircuit position upon movement of said sections from said open to saidclosed positions while said heat sealing means is relatively cool;second means connecting said heat sealing means to said switch means forautomatically operating the latter to open circuit position todeenergize said first means when said heat sealing means becomes heatedto a predetermined level while said sections are in said closedposition; latch means for maintaining said switch means in said opencircuit position after operation thereto by said heat sealing means;said switch means being operated automatically to said open circuitposition upon movement of said section to said open position; saidsecond means including a mechanical linkage movable by said heat sealingmeans upon expansion thereof to operate said switch means to said opencircuit position.

2. Heat sealing apparatus as set forth in claim 1, in which said linkageis constructed to amplify motion of said heat sealing means uponexpansion and contraction thereof.

3. Heat sealing apparatus as set forth in claim 2, in which said switchmeans includes a relatively movable and a relatively stationarycooperating contact; said movable contact being mounted for operation byone end of said linkage and said linkage having its other end secured tosaid heat sealing means.

4. Heat sealing apparatus as set forth in claim 3, in which said diemeans and said first means include a strip of metal constituting aresistance heater; one end of said strip being fixedly secured to saidfirst section and the other end of said strip being free to move anddrive said linkage as said strip expands during heating thereof.

5. Heat sealing apparatus as set forth in claim 4, in which, with saidsections in closed position, heating of said strip causes said movablecontact to wipe across said stationary contact until said strip heats tosaid predetermined level at which point said movable contact is drivenbeyond said stationary contact into engagement with said latch means.

6. Heat sealing apparatus as set forth in claim 5, in which there is abiasing means providing contact pressure as said movable contact wipesacross saidstationary contact, said biasing means also maintaining saidmovable contact in engagement with said latch means until subsequentoperation of said sections to said open position.

7. Heat sealing apparatus as set forth in claim 3, in which the linkagecomprises a bar mounted to a pivot located much closer to one end thanto the other end thereof; said other end of said strip being secured tosaid one end of said bar.

8. Heat sealing apparatus as set forth in claim 7, in which the linkagealso includes an arm secured at one end thereof to said other end ofsaid bar and being mounted on a pivot that is substantiallyperpendicular to the pivot for said bar; said movable contact being atthe other end of said arm.

9. Heat sealing apparatus as set forth in claim 8, in which with saidsections closed, heating of said strip causes said movable contact towipe across a face of said stationary contact until said strip heats tosaid predetermined level, at which point said movable contact ispositioned clear of said face; said movable contact having self biasingmeans providing contact pressure while said movable contact is inengagement with said face; said self biasing means operating saidmovable contact into engagement with said latch means when said l1. Heatsealing apparatus as set forth in claim 7 also including means forchanging the location of said pivot with respect to the ends of said barto adjust the heating level of said heat sealing means at which thelatter operates said switch means to said open circuit position.

Ik lk #I l#

1. Heat sealing apparatus including first and second support sections;means mounting said sections for relative movement between a closed, orsealing, position and an open, or work loading and unloading, position;heat sealing means including a die mounted to said first section andelectrically energized first means for heating said die; switch meansconnected in circuit with said first means for controlling energizationthereof; said switch means being operated automatically to closedcircuit position upon movement of said sections from said open to saidclosed positions while said heat sealing means is relatively cool;second means connecting said heat sealing means to said switch means forautomatically operating the latter to open circuit position todeenergize said first means when said heat sealing means becomes heatedto a predetermined level while said sections are in said closedposition; latch means for maintaining said switch means in said opencircuit position after operation thereto by said heat sealing means;said switch means being operated automatically to said open circuitposition upon movement of said section to said open position; saidsecond means incluDing a mechanical linkage movable by said heat sealingmeans upon expansion thereof to operate said switch means to said opencircuit position.
 2. Heat sealing apparatus as set forth in claim 1, inwhich said linkage is constructed to amplify motion of said heat sealingmeans upon expansion and contraction thereof.
 3. Heat sealing apparatusas set forth in claim 2, in which said switch means includes arelatively movable and a relatively stationary cooperating contact; saidmovable contact being mounted for operation by one end of said linkageand said linkage having its other end secured to said heat sealingmeans.
 4. Heat sealing apparatus as set forth in claim 3, in which saiddie means and said first means include a strip of metal constituting aresistance heater; one end of said strip being fixedly secured to saidfirst section and the other end of said strip being free to move anddrive said linkage as said strip expands during heating thereof.
 5. Heatsealing apparatus as set forth in claim 4, in which, with said sectionsin closed position, heating of said strip causes said movable contact towipe across said stationary contact until said strip heats to saidpredetermined level at which point said movable contact is driven beyondsaid stationary contact into engagement with said latch means.
 6. Heatsealing apparatus as set forth in claim 5, in which there is a biasingmeans providing contact pressure as said movable contact wipes acrosssaid stationary contact, said biasing means also maintaining saidmovable contact in engagement with said latch means until subsequentoperation of said sections to said open position.
 7. Heat sealingapparatus as set forth in claim 3, in which the linkage comprises a barmounted to a pivot located much closer to one end than to the other endthereof; said other end of said strip being secured to said one end ofsaid bar.
 8. Heat sealing apparatus as set forth in claim 7, in whichthe linkage also includes an arm secured at one end thereof to saidother end of said bar and being mounted on a pivot that is substantiallyperpendicular to the pivot for said bar; said movable contact being atthe other end of said arm.
 9. Heat sealing apparatus as set forth inclaim 8, in which with said sections closed, heating of said stripcauses said movable contact to wipe across a face of said stationarycontact until said strip heats to said predetermined level, at whichpoint said movable contact is positioned clear of said face; saidmovable contact having self biasing means providing contact pressurewhile said movable contact is in engagement with said face; said selfbiasing means operating said movable contact into engagement with saidlatch means when said movable contact is moved clear of said face byexpansion of said strip.
 10. Heat sealing apparatus as set forth inclaim 1 also including means for adjusting the heating level of saidheat sealing means at which the latter operates said switch means tosaid open circuit position.
 11. Heat sealing apparatus as set forth inclaim 7 also including means for changing the location of said pivotwith respect to the ends of said bar to adjust the heating level of saidheat sealing means at which the latter operates said switch means tosaid open circuit position.